Apparatus to study and photograph the ocular fundus have been on the market for many years under the term fundus camera and have become indispensable aids in ophthalmic diagnostics. They are used, for instance, to study the cardiovascular system using the so-called fluorescein angiography, to diagnose intraocular tumors, to detect vessels damaged by diabetes, to detect detached retinae, etc. In any case, what matters is to obtain an image in which even the finest vessel structures are still discernible.
In the known fundus cameras, the ocular fundus is illuminated by means of a light beam projected on the pupil of the eye, and the light reflected from the eye's retina is directed to an observation microscope for image formation. These devices have meanwhile reached their limits in terms of further improvement possibilities, in particular since the patient's strain-bearing capacity cannot be increased further.
For diagnostic reasons, however, it is desirable to obtain images of the ocular fundus having a still better resolution and improved contrast, while at the same time reducing the strain on the patient as far as possible.
An attempt to progress in this direction is described in U.S. Pat. No. 4,213,678. In the device described in this patent, a collimated laser beam focused through the eye is used for the illumination of a single point on the retina, the beam being deflected in a manner resulting in a sequential point-by-point scanning of the retina in the form of a line-scanning pattern. The light reflected from the retina and passing through the full pupil of the eye is directed to a photoelectric receiver. Its signal output is synchronized with the scanning motion of the laser beam and serves to generate an image on a television monitor.
While in contrast to a fundus camera this known device reduces the strain to which the patient is exposed, it cannot provide a substantial increase in the resolution since the laser beam, due to diffraction, illuminates a relatively large area of the retina (10 .mu.m in diameter, approximately).
This disadvantage cannot be eliminated by improving the external optical imaging system, because the imaging media of the optical apparatus of the eye are invariably affected by optical aberrations. Nor does a magnified representation of a partial area of the retina, to which in this known device the selected scanning field has to correspond, result in a substantial improvement of the achievable resolution. Because of the limited point resolution of the resonant galvanometer scanner used, this known arrangement does not permit the simultaneous generation and representation of both an overview image and an image part of high resolution.